Face to faces ... a gallery visitor has a closer look at Francis Bacon's Three Studies for a Portrait of George Dyer, 1963, part of Tate Britain's Bacon retrospective. Photo: Andy Rain/EPA

Visiting the big new Francis Bacon exhibition at London's Tate Britain this week, I was assailed by what I can only describe as a repressed memory - a memory which is bizarre in the extreme, and entirely shaming and unedifying.

I was in Room 6 of the exhibition, which the curators have entitled "Archive", because it attempts to excavate Bacon's working practices, and shows the way he uses found images and pictures ripped from magazines: photographs and stills from movies. Famously, Bacon was inspired by Eisenstein's Battleship Potemkin, particularly the nurse with the broken spectacles, which he transformed into his characteristically disquieting 1957 painting Study For The Nurse From The Battleship Potemkin.

The exhibition displays Bacon's copy of Film, a 1946 Pelican publication by movie historian Roger Manwell, which shows stills from the famous Odessa Steps Sequence, including of course the nurse, which so transfixed Bacon. Intriguingly, the exhibition juxtaposes Bacon's copy of this battered paperback with his copy of a book called Phenomena of Materialism: A Contribution to the Investigation of Mediumistic Teleplastics, by Baron Von Shrenk Notzing. This contains blurry images of what appear to be strange contorted apparitions - again, grist to Bacon's mill.

Looking at this, I pondered Bacon's perception that still movie images detached from a motion picture sequence have an uncanny, deathly quality: undead, zombie forms deprived of the "life" that the moving picture gave them, yet not entirely dead - and also ghostly. I duly made note of all this, before suddenly being assailed by an extraordinary memory. I remembered that I can claim something that very few non-specialists can claim, and perhaps very few art historians.

I had once spoken to Francis Bacon on the telephone.

It was in 1990, and I was in my first job after leaving university: doing shifts on the Londoner's Diary of the London Evening Standard. In those days, the Diary was edited by a notorious figure, Rory Knight Bruce, reputedly the model for the character "Rory Plantagenet" from Martin Amis's novel The Information. Rory was an eccentric figure, to say the very least; passionately dedicated to hunting and with a fiery temper, he was the master of foxhounds of the United Pack in Shropshire and hunted about two or three days a week, coming to London for the rest of the time to edit the column.

On what would have been my first week there, he peremptorily informed me of my assignment of the morning: I was to write a full-blooded attack on the Turner prize - or rather, I was to persuade some public figure to attack the Turner prize on the column's behalf, and this would constitute our "story" of the day.

"Is it really acceptable ... " Rory declaimed, "... that a collection of loathsome art-crowd inverts should use the name of Turner to lend substance to this appalling and valueless charade? Peter, I want you to telephone Francis Bacon and put that to him. Get him to attack the Turner prize! Attack it, attack, attack!"

Blandly, I prepared to telephone Francis Bacon's agent, or his dealer, and leave this message, and resign myself to naturally never being called back. But Rory had something up his sleeve.

"Here is Francis Bacon's private telephone number!" he hissed, scribbling it on my pad. "Dial it, and destroy it immediately. Do not put it in your contacts book!"

But of course I did, and I dug this book up today, 18 years after the event, and here is the number: 071-584 2925. Francis Bacon's home telephone number, the number at his legendary chaotic studio in South Kensington, the studio that has since been dismantled and reverently reconstructed in the Hugh Lane Gallery in Dublin. How on earth had Rory Knight Bruce got Francis Bacon's home number? Well, Rory had a certain epicene handsomeness in his youth, and was rumoured to frequent the Colony Room Club in Soho, a haunt of Bacon's ...

At any rate, I was now expected to telephone the world's greatest living artist, then 81 years old, actually to interrupt him in the middle of his work, with the most extraordinarily fatuous and offensive question surely ever posed by a journalist.

Utter silence fell on the desk as all the other reporters realised what it was I was supposed to do. Pleadingly, I glanced over at Rory's deputy, Marcus Scriven, who had relatively recently joined the column after having been a captain in the Welsh Guards. He grinned at me cheerfully: "Public service journalism, old boy!"

I could feel myself going wobbly and pale, a sweating, traumatised carcass, like one of Bacon's own figures. With fingers like chippolatas, I stabbed out the number: 071-584 2925. There was a brief silence, while I prayed for an "engaged" or "unobtainable" signal. Then it rang - for a long time. Then someone picked up, and said: "Yes?" on a quavering, rising tone.

"Is that Mr Francis Bacon?" I squeaked.

"Yes," he replied, in the same rising tone.

"Erm, this is Peter Bradshaw from the Londoner's Diary page in the Evening Standard."

Again: "Yes?"

I looked over at Rory who was fixing me with his Ancient Mariner's gaze. There was no backing out.

"Could you tell me, Mr Bacon - do you think it objectionable that a crowd of loathsome art-crowd inverts should abuse the name of 'Turner' for their prize?" I gabbled, feeling quite sure that my place in hell was now utterly assured.

There was silence, and then, thankfully Bacon began to laugh. "I'm awfully sorry, Mr Bradshaw, but I'm afraid I cannot help you!" And he replaced the receiver.

I went over and told Rory what Francis Bacon had said to me.

"Oh Christ, that's no fucking good!" he spluttered. "No fucking good at all. Fuck me. Look, I'm going to lunch. If the editor comes in, tell him I'm out on a story. Fuck!" He left. It was 11:45am.

In Room 10 of the Tate exhibition (entitled "Late") one can see Francis Bacon's last triptych from 1991, the painting that he may well have been working on when I telephoned. The catalogue observes of this piece: "He faced death with a defiant concentration on the exquisiteness of the lived moment." How remarkable to think that his concentration on this moment was interrupted by a grotesque person from Porlock.

But there it is: his number. If I update it to 020-7584 2925, and call it - well, perhaps a ghostly phone will ring in that studio, reconstructed in Dublin, and a polite elderly voice will answer, lose patience, and tell me to bugger off.

Join Guardian art critic Jonathan Jones on a walking tour through Tate Britain's Francis Bacon retrospective, and discover how the Irish-born painter emerged as one of the greatest artists of the 20th century